The study continues investigations into the nature of energy metabolism in the fetus. A chronic fetal lamb preparation and a chronic nonhuman primate model, the fetal baboon, are being used to extend previous studies of quantitative energy metabolism. Substrate uptake and production by the fetal animals is being evaluated by utilizing appropriately placed arterial and venous catheters for sampling arteriovenous metabolic differences, radioactive precursor tracer techniques, and measures of fetal blood flow and specific organ blood flows. We plan to study the capacity of the fetus to control gluconeogenesis, glycogenesis, and glycogenolysis in the face of a hostile maternal metabolic milieu, focusing particularly on endogenous hormonal or substrate mediated control mechanisms. In addition, pharmacologic probes of hormonal control mechanisms will be employed during steady state conditions in the pregnant animal. These studies are immediately relevant to the clinical problems of the infant of the diabetic mother, who may be exposed to acute hypoglycemia, or acute and chronic hyperglycemia, and to the infant of the calorically deprived, undernourished mother.